The present application claims priority to Japanese Application No. P10-173308 filed Jun. 19, 1998, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to a semiconductor light emitting device and its manufacturing method.
2. Description of the Related Art
Known as a sort of semiconductor lasers are so-called etched mirror lasers whose cavity edges are cut surfaces made by etching, or pseudo surface-emitting lasers incorporating raising mirrors into such etched mirror lasers. In these etched mirror lasers and pseudo surface-emitting lasers, heretofore used is a multi-layered film coating technology similar to a technology used in cleaved lasers having cleaved surfaces as their cavity edges, for controlling their refractive indices to increase or decrease refractive indices of their cavity edges.
The multi-layered coating technology is one of technologies already established and indispensable for controlling refractive indices of cavity edges of cleaved lasers which are processed for each bar divided from a wafer.
However, the multi-layered film coating technology is not always suitable for devices, such as etched mirror lasers or pseudo surface-emitting lasers whose cavity edges can be made in a wafer process using dry etching and not by cleavage.
More specifically, if a multi-layered thin-film coating is applied to cavity edges still held on a wafer, then particles of a coating material enter largely aslant (with a large incident angle) relative to the cavity edge, and the profile of the thickness of the coating film is liable to become uneven along the wafer surface.
Therefore, in order to prevent such uneven profile of the film thickness, the process of multi-layered thin-film coating on the cavity edges cannot be conducted while the product still maintains the state of a wafer, but had to follow after the wafer was cleaved into bars. As a result, the conventional technique could not make use of the advantage of etched mirror lasers that all can be manufactured in a wafer process, without coating.
Moreover, a GaN semiconductor laser capable of emitting blue-violet light was developed recently (for example, S. Nakamura, et al., Appl. Phys. Lett. 72, 211(1998)), and it is expected that semiconductor lasers will be progressed in shortening their emission wavelengths toward the ultraviolet region. However, although multi-layered thin-film coating techniques have been established for AlGaAs semiconductor lasers having emission wavelengths in the band of 800 nm, it will be difficult to employ them particularly for fabrication of high-power semiconductor lasers due to insufficient materials with high refractive indices, which are transparent in the above-mentioned short wavelength region. Also in semiconductor lasers for other wavelength bands, it will be difficult to control edge reflectance unless appropriate multi-layered thin-film coating materials are provided.
It is therefore an object of the invention to provide a semiconductor light emitting device easily controlled in reflectance of cavity edges and a manufacturing method capable of easily manufacturing such a semiconductor light emitting device.
According to the first aspect of the invention, there is provided a semiconductor light emitting device comprising a rugged structure including concave portions and/or convex portions made on at least one of cavity edges of a cavity thereof to extend substantially in parallel with bonded surfaces of semiconductor layers forming the cavity.
According to the second aspect of the invention, there is provided a semiconductor light emitting device comprising a rugged structure including dot-shaped concave portions and/or convex portions made on at least one of cavity edges of a cavity thereof.
According to the third aspect of the invention, there is provided a method for manufacturing a semiconductor light emitting device having a rugged structure including concave portions and/or convex portions made on at least one of cavity edges of a cavity thereof to extend substantially in parallel with bonded surfaces of semiconductor layers forming the cavity, comprising:
forming the rugged structure by making the concave portions on the cavity edge by etching, utilizing differences in chemical property among these semiconductor layers forming the cavity caused by differences in composition among them or the presence or absence of distortion at bonded interfaces thereof.
In the present invention, reflectance of the cavity edge having formed the rugged structure is controlled by repetitive distance of the concave portions or convex portions of the rugged structure, depth of the concave portions of height of the convex portions in the rugged structure, duty ratio of the rugged structure, and cross-sectional configuration of the rugged structure. In this case, reflectance of the cavity edge having formed the rugged structure can be controlled so that opposite cavity edges of the cavity be different in reflectance.
In the present invention, both cavity edges of the cavity may have the rugged structures. In this case, it is possible to control values of reflectance of the respective cavity edges independently by independently determining the repetitive distance of the concave portions or convex portions of the rugged structure, depth of the concave portions of height of the convex portions in the rugged structure, duty ratio of the rugged structure, and cross-sectional configuration of the rugged structure for respective cavity edges such that, for example, one of the cavity edges has a lower reflectance while the other cavity edge has a higher reflectance. Additionally, the first and second aspects of the invention may be combined to make on one of the cavity edges the rugged structure including concave portions and/or convex portions extending substantially parallel with bonded surfaces of the semiconductor layers forming the cavity and make on the other cavity edge the rugged structure including dot-shaped concave portions and/or convex portions. Alternatively, it is also possible to make on one of the cavity edges the rugged structure including concave portions and/or convex portions extending substantially in parallel with bonded surfaces of the semiconductor layers forming the cavity or the rugged structure including dot-shaped concave portions and/or convex portions while making on the other cavity edge a rugged structure including concave-portions and/or convex portions extending substantially vertically of bonded surfaces of the semiconductor layers forming the cavity.
In the present invention, the repetitive distance of concave portions and/or convex portions in the rugged structure is preferably shorter than the wavelength of outgoing light from the cavity edge from the viewpoint of preventing that the outgoing light from the cavity edge is diffracted by the rugged structure.
In the present invention, the cavity edge having formed the rugged structure may be coated with a single-layered or multi-layered film. This is useful because the coating film on the cavity edge functions as a passivation film to improve reliability of the cavity edge and adjust the edge reflectance.
In the present invention, the rugged structure may be formed, for example, either by making concave portions on the cavity edge by etching or by stacking a film to make convex portions on the cavity edge.
According to the first aspect of the invention having the above-explained features, since at least one of cavity edges of the cavity has formed the rugged structure including concave portions and/or convex portions extending substantially in parallel with bonded surfaces of semiconductor layers forming the cavity, reflectance of the cavity edge can be controlled easily without using multi-layered thin-film coating techniques.
According to the second aspect of the invention having the above-explained features, since at least one of cavity edges of the cavity has formed the rugged structure including dot-shaped concave portions and/or convex portions, reflectance of the cavity edge can be controlled easily without using multi-layered thin-film coating techniques, similarly to the first aspect of the invention.
According to the third aspect of the invention having the above-explained features, when manufacturing the semiconductor light emitting device according to the first aspect of the invention, by forming the rugged structure by making concave portions on the cavity edge by etching, utilizing differences in chemical property among semiconductor layers forming the cavity caused by differences in composition among these semiconductor layers or the presence or absence of distortion at the bonded interfaces of the semiconductor layers, a repetitive distance of concave portions or convex portions of the rugged structure and a duty ratio of the rugged structure can be realized with a remarkable reproducibility. Especially when the semiconductor light emitting device to be manufactured is an etched mirror laser having etching edges as its cavity edges, all can be manufactured in a wafer process. Therefore, this is particularly effective when used for manufacturing etched mirror lasers.